The purpose of this project is to explore the quality of information that results from conduction trials of experimental therapies for AIDS in community settings. Traditionally drug trials are conducted in tightly controlled medical care settings. Because of the nature of HIV disease-- its long latency period and the fact that there are no effective cures-- there has been increased pressure on the biomedical community to broaden the availability of experimental treatments. Recently, government and privately funded programs have established studies following the progression of the disease and testing new therapies in community medical care settings. This study will test the quality of data emanating from those studies to determine whether factors existing in the community that are not found in the medical research center environment seriously affect the results of the studies. If such biases or sources of error are found to exist, then study designs can be modified to improve the reliability of these results in the future. The characteristics of two groups of HIV infected patients will be compared: those enrolled in simple follow-up studies of disease progression, who receive standard therapies for HIV related disorders, and those who are selected to participate in clinical experiments. This study will examine the characteristics of both groups. The appearance of significant differences in characteristics between the two groups could indicate biases that jeopardize the validity of the results of these studies. The effects of any such biases will also be measured.